The present invention relates, as indicated, to a brush construction and, more particularly, relates to an improved ferrule brush form that increases the tenacity with which the bristle is secured in the brush.
In a conventional bristle brush the bristle may comprise an assemblage of individual elongate bristle filaments, which may either be natural or synthetic filaments, fibers or the like. The bristle has a tip end for applying fluid-like material to a surface and a bottom or inner end, referred to as the butt end, secured in a generally tubular, longitudinally extending ferrule, for example, using epoxy or equivalent hardenable adhesive material. A handle or other holder also is usually connected to extend from the top of the ferrule for manipulating the brush. In the case of the bristle comprising an assemblage of parallel filaments, the respective butts or bottom extremities of the filaments are usually so closely packed in the ferrule as to form a substantially flat, almost solid surface area. The adhesive material later poured into the ferrule usually only penetrates the bristle for a distance of approximately one-eighth inch to one-fourth inch and bonds only with the bristle at that limited surface area.
To strengthen the ferrule, which is usually formed of sheet metal, plastic or other relatively thin material, one or more annular beads may be formed in the tubular wall of the ferrule extending peripherally thereabout generally perpendicularly with respect to the longitudinal extent of the ferrule. Such beads have had a relatively small semi-circular cross-sectional profile, which do not affect the close-packed compaction of the bristle hold end in the ferrule, and the bristle hold usually extends upwardly into the ferrule past at least one of the beads, for example, as in U.S. Pat. No. 3,155,998. In the brush structure disclosed in that patent the bristle hold preferably terminates between the two beads, and the epoxy resin flows into the upper bead and hardens therein to lock the hardened material in place in the ferrule. Also, the beads disclosed in that patent have relatively small cross-sectional profiles that would not provide for expansion of the bristle were the latter to terminate therein; nor would they permit the epoxy resin appreciably to flow into and about the bristle hold.
Since the individual elongate bristle filaments usually are tapered such that the butt end of each is appreciably larger in cross section than the tip end, and since a tubular ferrule normally will apply its shear holding force to the bristle filaments at the butt end or bottom extremities thereof where they are most closely packed, the bristle may assume a generally spreading or toe-out natural shape in a direction toward the filament tips. Such a toe-out shape is usually undesirable. Wood, cardboard or the like spacer inserts are usually placed between groups of filaments of the bristle at the butt end both to save material by reducing the required number of filaments to fill the ferrule opening area, to control the shape of the bristle reducing the flare or toe-out tendency thereof, and to provide a space inside the brush to act as a paint reservoir.